If it is green stay home, if it is clear then it isn't generally infectious.

DD has a chronic cough due to respiratory issues, so we do go to things when she is coughing, but if there is any hit of snot we stay away, still makes me feel horrible when she sounds like she is coughing up a lung, but now we know it isn't infectious most of the time, unless she gets a respiratory infection, then it is a lock down.

See how he is in the morning and make your call then